LCD device and method for manufacturing the same

ABSTRACT

A pair of dummy orientation film patterns are provided for an orientation film used for aligning LC molecules in an LCD device. For a rubbing treatment of the orientation film, a rubbing cloth is cleaned by one of the dummy orientation film patterns before rubbing the orientation film, and also cleaned by the other of the dummy orientation film patterns after rubbing the orientation film thereby preparing next rubbing treatment for the next LCD device. The dummy orientation film pattern has a thickness larger than the thickness of the orientation film.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to an LCD (liquid crystal display)device and a method for manufacturing the same, and more particularly,to the structure of an LCD device having an orientation film suited to arubbing treatment.

[0003] (b) Description of the Related Art

[0004] As is well known, an LCD device has a pair of substratessandwiching therebetween an LC layer, wherein at least one of thesubstrates is transparent. By applying a voltage onto the LC layer tochange the alignment state of the LC molecules, a desired image can bedisplayed on the LCD device while revealing the change of the alignmentstate by using a pair of polarizing plates.

[0005] An orientation film is generally used as a means for aligning theaxes of LC molecules in a specified direction. The orientation film isobtained by a rubbing treatment wherein the orientation film is rubbedwith a rubbing cloth such as rayon to form a plurality of minute stripegrooves on the surface of the orientation film. The LC molecules stayingin contact with the orientation film are aligned in the direction of thestripe grooves. The alignment of the LC molecules can be changed byapplying an external voltage onto the LC molecules thus aligned whileadjusting the magnitude of the external voltage, thereby changing theamount of light passing through the polarizing plates.

[0006] It is to be noted that the rubbing treatment of the orientationfilm by using the rubbing cloth may involve a problem in that theorientation film is attached with a foreign particle and a scratch isformed on the surface of the orientation film due to the presence of theforeign particle during the rubbing. The foreign particle or the scratchon the surface of the orientation film disturbs the alignment state ofthe LC molecules, thereby incurring an undesirable luminance spot or anuneven luminance on the screen of the LCD device.

[0007] To avoid the above problem of the orientation film, the rubbingcloth is generally subjected to cleaning before the rubbing treatment.Although the cleaning may completely remove the foreign particles fromthe rubbing cloth, the above problem itself cannot be completelyremoved. More specifically, the rubbing cloth my be attached with aforeign particle staying in the area other than the display area beforethe rubbing treatment of the subject orientation film, or may beattached with a foreign particle during the prior rubbing treatment ofanother orientation film. In particular, the vicinity of the edge of thesubstrate on which the orientation film is formed may be contaminated byan etching residue generated during etching a multilayer film, or by aforeign particle generated by peeling-off of the multilayer film in thevicinity of the edge.

[0008] Patent Publication JP-A-2001-318380 describes a particle removerformed on a substrate of an LCD device. FIG. 5 shows the rubbingtreatment in a perspective view, and FIG. 6 is a sectional view takenalong line VI-VI in FIG. 5. As shown in FIG. 5, the particle removers 42are disposed on both the front and rear edges of the substrate 40 onwhich an orientation film 41 is formed in the central area. The particleremover 42 extends in the direction normal to the direction in which thesubstrate advances during the rubbing treatment. As shown in FIG. 6, theparticle remover 42 is formed by depositing an insulator film 42 b on astripe film 42 a formed on the substrate 40, and includes a lineargroove 42 c formed on the insulator film 42 b and a protrusion 42 ddisposed in the vicinity of the linear groove 42 c on the insulator film42 b.

[0009] The stripe film 42 a is made of chrome which is generallydeposited as a material for a black matrix for shielding the TFTs etc.,whereas the insulator film 42 b is made of silicon oxide which isdeposited as an insulating film for the TFTs. The particle remover 42has a length larger than the width of the orientation film 41.

[0010] In the rubbing treatment, as shown in FIG. 5, the substrate 40 ismoved in the direction of arrow for rubbing by a rubbing cloth 11, whichfirst contacts with the particle remover 42 before the rubbingtreatment. The particle remover 42, as shown in FIG. 6, removes theparticles 13 from the rubbing cloth 11 at the linear groove 42 c and theprotrusion 42 d, whereby the rubbing cloth 11 is cleaned and theneffects a rubbing treatment for the orientation film 41.

[0011] The conventional technique shown in FIGS. 5 and 6, however,complicates the fabrication process for the LCD device due to formingthe particle removers 42 on the substrate 40 on which the orientationfilm 41 is formed. In addition, the particles removed by the particleremover 42 may contaminate the orientation film 41 by entering the areafor the orientation film 41 during or after the rubbing treatment.

[0012] Patent Publication JP-A-9(1997)-43629 describes a dummy electrodearea outside the display area, for removing particles generated by arubbing treatment by a rubbing cloth. More specifically, as shown inFIG. 7, the LCD device includes a TFT substrate 40 and a countersubstrate (not shown) sandwiching therebetween a LC layer and bondedtogether by using a sealing. The counter substrate includes a counterelectrode along the alignment surface thereof.

[0013] The TFT substrate 40 has a transparent conductive film, andincludes a central display area 46 and a peripheral dummy electrode area47. As shown in FIG. 8, the central display area 46 includes therein anarray of pixel electrodes 43 and associated TFTs acting as switchingdevices for the pixel electrodes 43. The peripheral dummy electrode area47 includes therein a plurality of dummy electrodes 44 arranged in anarray extending from the pixel electrodes 43 in the display area 46. Athin orientation film 41 made of polyimide, for example, is formed onthe entire area of the TFT substrate 40 by using a printing technique.

[0014] The orientation film 41 is rubbed by a rubbing cloth 11 attachedonto a roller 10. The foreign particles generated by the initial stageof the rubbing treatment by the rubbing cloth 11 are captured in thegroove formed between the dummy electrodes 44 in the peripheral dummyelectrode area 47, to thereby reduce the particles to be captured in thegroove formed between the pixel electrodes 43 in the central displayarea 46. This reduces the possibility of a short-circuited failurecaused by the particles captured between the pixel electrodes 43 in thedisplay area 46.

[0015] The particles generated by the rubbing treatment are captured inthe groove formed between the dummy electrodes 44, which are arranged ata specified pitch. The number of dummy electrodes for capturing theparticles is limited, and accordingly, the amount of particles capturedbetween the dummy electrodes 44 is not sufficient. In addition, theparticles captured between the dummy electrodes may move to the centraldisplay area 46 to degrade the image quality of the LCD device.

SUMMARY OF THE INVENTION

[0016] In view of the above problems in the conventional technique, itis an object of the present invention to provide an LCD device which iscapable of providing a higher image quality after rubbing treatment ofthe orientation film.

[0017] The present invention provides an LCD device including an LClayer and first and second substrates sandwiching therebetween the LClayer, each of the first and second substrates mounting thereon anorientation film in a display area and a dummy orientation film patternin a peripheral area, the dummy orientation film pattern being disposedapart from the orientation film.

[0018] The present invention also provides a method for manufacturing anLCD device including the steps of: forming a dummy orientation filmpattern in a peripheral area apart from an orientation film formed in adisplay area; rubbing the orientation film with a rubbing cloth; rubbingthe dummy orientation film pattern with the rubbing cloth.

[0019] In accordance with the LCD device and the method of the presentinvention, the dummy orientation film pattern disposed apart from theorientation film allows the rubbing cloth for rubbing the orientationfilm to be cleaned from foreign particles, and the foreign particlescaptured by the dummy orientation film pattern scarcely enter thedisplay area due to the arrangement of the dummy orientation filmpattern apart from the orientation film.

[0020] It is preferable that the dummy orientation film pattern includea plurality of stripe films extending parallel to one another, and thatthe stripe films have a thickness larger than a thickness of theorientation film. This improves the efficiency for capturing the foreignparticles by the dummy orientation film pattern and further prevents theforeign particles captured in the dummy orientation film pattern fromentering the orientation film.

[0021] The above and other objects, features and advantages of thepresent invention will be more apparent from the following description,referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a perspective view of a rubbing treatment for rubbing anLCD device according to an embodiment of the present invention.

[0023]FIG. 2 is a sectional view of the rubbing treatment of FIG. 1taken along line II-II in FIG. 1.

[0024]FIG. 3 is a sectional view of a modified rubbing treatmentmodified from FIG. 2.

[0025]FIG. 4 is a schematic side view of a flexo-graphic printing systemfor forming the orientation film by using a printing technique.

[0026]FIG. 5 is a perspective view of a conventional LCD device, showinga rubbing treatment of an orientation film by using a rubbing cloth.

[0027]FIG. 6 is a sectional view taken along line VI-VI in FIG. 5.

[0028]FIG. 7 is a top plan view of another conventional LCD device.

[0029]FIG. 8 is a sectional view of the LCD device of FIG. 7 during arubbing treatment thereof.

PREFERRED EMBODIMENTS OF THE INVENTION

[0030] Now, the present invention is more specifically described withreference to accompanying drawings, wherein similar constituent elementsare designated by similar reference numerals throughout the drawings.

[0031] Referring to FIG. 1, there is shown a rubbing treatment of anorientation film 22 formed on a TFT substrate 21, wherein theorientation film 22 is moved in the direction of arrow 20 by a rubbingstage 12 and subjected to a rubbing treatment by a rubbing cloth 11. Therubbing cloth 11 is attached onto the surface of a rubbing roller 10rotating around a rotational axis 13 thereof.

[0032] Referring to FIG. 2, orientation film 22 is disposed in thedisplay area 26 of the TFT substrate 21. The dummy orientation filmpattern 23 is disposed in the peripheral area, i.e., in the vicinity ofeach of the front edge and the rear edge of the TFT substrate 21, asviewed in the moving direction 20 of the TFT substrate 21 with respectto the rubbing cloth 11 during the rubbing treatment. Each dummyorientation film pattern 23 includes a pair of stripe films 23 aextending in the direction normal to the moving direction 20 of the TFTsubstrate 21 and a depression 23 b formed between the stripe films 23 a.

[0033] The surface of the orientation film 22 is rubbed with the rubbingcloth 11 and thus provided with minute stripe grooves thereon by therubbing cloth 11. It is to be noted that the dummy orientation filmpattern 23 formed in the peripheral area 27 of the TFT substrate 21 isfirst contacted with the rubbing cloth 11 before the orientation film 22reaches the rubbing cloth 11.

[0034] The stripe films 23 a in the dummy orientation film pattern 23have a thickness of 2000 angstroms at a maximum whereas the orientationfilm 22 has a thickness of 300 to 1200 angstroms. The stripe films 23 ain the dummy orientation film pattern 23 extend beyond the lateral edgesof the orientation film 22. The dummy orientation film pattern 23 has afunction of removing foreign particles from the rubbing cloth 11 due tothe larger thickness of the stripe films 23 a in the dummy orientationfilm pattern 23.

[0035] The dummy orientation film pattern 23 is contacted with therubbing cloth 11 during the movement of the TFT substrate 21. The frontdummy orientation film pattern 23 disposed in the front peripheral areaof the TFT substrate 21 removes foreign particles, if any, from therubbing cloth 11 for cleaning the rubbing cloth 11 in advance, as shownin FIG. 2. The orientation film 22 is then contacted with the cleanedrubbing cloth 11 for forming the minute stripe grooves on the surface ofthe orientation film 22. The rubbing cloth 11 then contacts with therear dummy orientation film pattern 23 formed in the vicinity of therear edge of the TFT substrate 21. If a foreign particle is attachedonto the rubbing cloth 11 during the rubbing treatment of theorientation film 22, the foreign particle is also removed from therubbing cloth 11 by the rear dummy orientation film pattern 23 forpreparing the next rubbing treatment.

[0036] The dummy orientation film pattern 23 is formed by aflexo-graphic printing technique using organic polyimide, which is alsoused as a material for forming the orientation film 22 in the displayarea 26.

[0037] The number of stripe films 23 a in each dummy orientation filmpattern 23 may be one or more. The stripe films 23 a may be cut at aplurality of points in the extending direction thereof. In the lattercase, it is preferable that the rubbing roller 10 be inclined withrespect to the surface of the TFT substrate 21 in view of the efficientremoval of the foreign particles.

[0038] Referring to FIG. 3, a modified dummy orientation film pattern 24modified from the dummy orientation film pattern 23 of the aboveembodiment has a plurality of stripe films 24 a having differentthicknesses. More specifically, one of the stripe films 24 a disposedoutside another of the stripe films 24 a in the dummy orientation filmpattern 24 has a thickness larger than the thickness of the another ofthe stripe films 24, which has a thickness larger than the thickness ofthe orientation film 22. The innermost one of the stripe films 24 a, asdepicted in FIG. 4, has a thickness equal to the thickness of theorientation film 22. Other configurations are similar to those of theabove embodiment shown in FIGS. 1 and 2.

[0039] The smaller thickness of the inner stripe film 24 a as well asthe equality between the thickness of the innermost stripe film 24 a andthe thickness of the orientation film 22 is employed in view that thetips of the rubbing cloth 11 do not jump at the innermost stripe film 24a during the movement of the TFT substrate 21. The jump of the rubbingcloth 11 may let the foreign particles attached thereto to fly onto theorientation film 22.

[0040] Referring to FIG. 4, there is shown the procedure of theflexo-graphic printing system for forming the orientation film 22 andthe dummy orientation film pattern 23 or 24 on the TFT substrate 21 by aprinting technique. A flexo-graphic printing block 32 made of rubber isattached onto the surface of a transcribing roller 31, which iscontrolled to roll on the TFT substrate 21 mounted on a printing stage33. The material, organic polyimide, for forming the orientation film iscarried by the flexo-graphic printing block 32 and then attached ontothe TFT substrate 21 by printing to form the orientation film 22 and thedummy orientation film pattern 23 or 24 on the TFT substrate 21. Forthis purpose, a suitable amount of liquid polyimide is dropped onto thesurface of a doctor roll 35, which transfers the dropped polyimide tothe flexo-graphic printing block 32 on the transcribing roller 31through an anilox roll 36.

[0041] The anilox roll 36 has a quadrangular-pyramid groove assemblyhaving a lattice structure including 400 grooves per inch and a depth of10 to 20 micrometers, although it is not specifically shown in thedrawing. The polyimide is temporarily stored in the grooves, andtranscribed onto the flexo-graphic printing block 32 upon the contactbetween the anilox roll 36 and the flexo-graphic printing block 32 onthe transcribing roller 31. The flexo-graphic printing block 32 hasthereon a large number of minute protrusions forming a specifiedpattern, which elastically deform upon the contact to eject thepolyimide stored in the depressions between the minute protrusionstoward the TFT substrate 21, thereby forming a pattern of theorientation film 22 and the dummy orientation film pattern 23 or 24.

[0042] For forming a dummy orientation film pattern 23 having a largerthickness than the thickness of the orientation film 22, suitabledesigns are selected for the number and the depth of the grooves formedon the anilox roll 36 and the density and the height of the minuteprotrusions formed on the flexo-graphic printing block 32.

[0043] A method for fabricating the LCD device having the orientationfilm 22 and the dummy orientation film pattern 23 as described abovewill be described hereinafter with reference to FIGS. 1 and 2.

[0044] The TFT substrate 21 mounting thereon the orientation film 22 andthe dummy orientation film pattern 23 is mounted on the rubbing stage12, as shown in FIG. 1. The TFT substrate 21 is then moved toward therotating rubbing roller 10, thereby allowing the front dummy orientationfilm pattern 23 to pass by the rubbing cloth 11 while removing foreignparticles from the rubbing cloth 11, as shown in FIG. 2. The rubbingcloth 11 then contacts with the orientation film 22 for allowing theorientation film 22 to be subjected to a rubbing treatment. Further, theTFT substrate 21 is moved in the direction of arrow 20 to allow the rearorientation film pattern 23 to pass by the cleaning cloth 11, therebyremoving foreign particles 13, if any, from the rubbing cloth 11. Therubbing cloth 11 is thus prepared for a rubbing treatment for the nextTFT substrate.

[0045] The peripheral areas of the TFT substrate 21 are preferably cutfrom the TFT substrate 21 after the rubbing treatment to reduce thedimensions of the TFT substrate 21 in the final product of the LCDdevice.

[0046] In the above embodiments, the larger thickness of the dummyorientation film pattern 23 or 24 effectively removes the foreignparticles from the rubbing cloth 11. In addition, the arrangement of thedummy orientation film pattern 23 apart from the orientation film 22prevents the foreign particles captured by the dummy orientation filmpattern from entering the orientation film 22 in the central displayarea 26 after the rubbing treatment.

[0047] Since the dummy orientation film pattern 23 or 24 and theorientation film 22 are formed in a single printing process, theprocedure for forming the dummy orientation film pattern 23 or 24 doesnot substantially complicate the fabrication process for the LCD device.The configuration that the stripe films 24 a have reduced thicknessestoward the orientation film 22 prevents the particles attached onto therubbing cloth 11 from entering the orientation film 22 due to the jumpof the rubbing cloth 11.

[0048] Since the above embodiments are described only for examples, thepresent invention is not limited to the above embodiments and variousmodifications or alterations can be easily made therefrom by thoseskilled in the art without departing from the scope of the presentinvention. For example, the stripe film in the dummy orientation filmpattern may be curved to form a curved pattern or cut at a plurality ofpoints to form a dotted line pattern.

What is claimed is:
 1. An LCD device comprising an LC layer and firstand second substrates sandwiching therebetween said LC layer, each ofsaid first and second substrates mounting thereon an orientation film ina display area and a dummy orientation film pattern in a peripheralarea, said dummy orientation film pattern being disposed apart from saidorientation film.
 2. The LCD device according to claim 1, wherein saiddummy orientation film pattern includes a plurality of stripe filmsextending parallel to one another.
 3. The LCD device according to claim2, wherein said stripe films have a thickness larger than a thickness ofsaid orientation film.
 4. The LCD device according to claim 2, whereinone of said stripe films has a thickness larger than another of saidstripe films disposed nearer to said orientation film than said one ofsaid stripe films.
 5. The LCD device according to claim 4, wherein oneof said stripe films which is nearest to said orientation film has athickness equal to a thickness of said orientation film.
 6. The LCDdevice according to claim 1, wherein each of said first and secondsubstrates mounts thereon a pair of said dummy orientation filmpatterns.
 7. The LCD device according to claim 1, wherein said dummyorientation film pattern is made of a material same as a material forsaid orientation film.
 8. The LCD device according to claim 7, whereinsaid dummy orientation film pattern is made of polyimide.
 9. The LCDdevice according to claim 1, wherein said orientation film and saiddummy orientation film pattern are formed by a single flexo-graphicprinting process.
 10. A method for manufacturing an LCD devicecomprising the steps of: forming a dummy orientation film pattern in aperipheral area apart from an orientation film formed in a display area;rubbing said orientation film with a rubbing cloth; and rubbing saiddummy orientation film pattern with the rubbing cloth.
 11. The methodaccording to claim 10, wherein a pair of said dummy orientation filmpatterns are formed near the opposite edges of said orientation film.12. The method according to claim 10, wherein said dummy orientationfilm pattern includes a plurality of stripe films extending parallel toone another.
 13. The method according to claim 12, wherein said stripefilms have a thickness larger than a thickness of said orientation film.14. The method according to claim 12, wherein one of said stripe filmshas a thickness larger than another of said stripe films disposed nearerto said orientation film than said one of said stripe films.
 15. Themethod according to claim 14, wherein one of said stripe films which isnearest to said orientation film has a thickness equal to a thickness ofsaid orientation film.